In different kinds of motor vehicles, bicycles, machine equipments such as machine tools or the like, a transmission is widely used for altering input and output transmission ratios to attain a desired acceleration or deceleration.
A conventional transmission basically consists of different gears of various sizes. For example, a manual or an automatic transmission for a motor vehicle may provide a 4- to 5-speed transmission, in which each speed section needs to shift in a stepped manner, namely to shift from an upper section to a lower section and then from the lower section to a next section, such an operation process would be quite complicated, and sometimes a momentary failure might occur during the shifting process.
As far as a simple transmission for a bicycle is concerned, this transmission adopts usually a so-called conical pulley having a plurality of chain wheels of diameters varying in magnitude sequentially, the transferring of the chain among various chain wheels is quite unsmooth, resulting in a relatively long time for speed variation, and a failure might occasionally occur.
Among the commercially available continuously variable transmissions, a continuously variable transmission of belt-type is desirable, which is formed by having a belt covering on two wheels which are capable of changing the diameter of a V-shaped slot. This type of transmission has advantages of being simple in structure and easy in speed variation; but both ends of the belt are subject to a huge friction during operation, such that the belt is continuously bent and straightened to an extent, and thus prone to wearout and outbreak, even energy loss. Such a belt-type continuously variable transmission is not suitable for use in motor vehicles having a large horsepower.